It is a well recognized problem with modern power generation plants, which require relatively large volumes of water for operation, that there is a potential loss of water from the adherence to and buildup of a variety of foreign substances on any surfaces exposed to the water or fluid medium, in general. The exposed surfaces include the inner surfaces of the water intake pipes, valves, fittings, heat exchangers, etc, and the outer surfaces of screens (rotary and bar), etc. Power generating plants and other manufacturing facilities which require the use of a particular medium, such as fresh water, have long sought an effective method of keeping the fluid transport system operational and free of any buildup of foreign organisms or debris.
One such foreign organism of particular concern and discovered recently is the D. polymorpha or zebra mollusk. The zebra mollusk is more commonly referred to as a zebra mussel. To illustrate the severity of the problem, the origin and problems associated with the zebra mussel has been documented in numerous magazines and periodicals including an article published in the December, 1990 issue of "Electrical World" on pages 72-74 and another article published in the July, 1990 issue of "The Atlantic Monthly" on pages 81-87. The information disclosed in these particular articles has been incorporated herein by reference thereto.
Prior to the present invention, when the fluid transport systems of present day technology exhibit any significant diminished capacity due to clogging by foreign substance buildup, one method used for cleaning the submerged piping system is pulling a dragging device through the submerged piping system to dislodge the buildups or clogs and subsequently to pull them through to the exit for manual cleanup. There are significant drawbacks to this prior art method which are readily apparent and would, for example, include the fact that this method is not only labor-intensive but time-consuming. Furthermore, this method cannot be accomplished continuously, but must be done on a regularly scheduled basis.
Another cleaning method which has been used for industrial facilities, such as water treatment plants, includes flushing the fluid transport system with relatively large quantities of chemicals. These chemicals are known to include chlorine and potassium chloride. While this prior art process can normally be conducted in a continuous manner, it is not efficient or cost-effective to induce large quantities of these chemicals into the fluid medium. Depending on the end use of the fluid, these chemicals, may themselves be detrimental. When this occurs, the chemical must be separated out.
As discussed in the above-referenced articles, at least three types of problems have already been identified with zebra mussel fouling in water intake systems. Initially, layers of attached mussels will reduce or block flow, even through large diameter piping, trash racks, and traveling screens. Eventually, shells or clumps of shells breaking free of their attachment sites can block openings in piping, heat exchangers, strainers, or traveling screens. Finally, attachment points of the organisms accumulate other debris which even further reduce water flow and serve as sites for corrosion.
At the present time, there are three EPA-approved chemical methods that have been tried in United States power plants. These chemical methods are chlorination, which has been the most discussed method in the incorporated articles; bromination, primarily Acti-brom, a Nalco Chemical Co. (Naperville, Ill.) product; and Betz Laboratories (Trevose, Pa.) Clam-Trol. Several other chemical treatments have been tried in laboratory tests, but not in a utility or industrial environment. As previously stated, chlorination is the most commonly used chemical control for zebra mussel fouling. It has been reported that continuous chlorination at 0.3 ppm not exceeding three weeks is required to achieve efficacy. However, intermittent chlorination programs that feed a few hours daily have generally been found to be ineffective. Using other chemicals, such as ozone, hydrogen peroxide, and potassium permanganate is possible. Use of these chemicals, however, is expensive, environmentally unsound, and/or impractical to distribute throughout a fluid transport system.
In terms of current technology, it has been reported that Detroit Edison is attempting to control zebra mussels by scraping and hydroblasting during its regular maintenance periods. Janiece Romstadt has received permission from the Federal government to use a commercial mollucicide. Ontario Hydro is treating some of its coolant with hypochlorite, an oxidant that eats away at the soft parts of the organism and is the active ingredient in household bleach. Ontario Hydro admits, however, that this short-term solution is offensive to a public anxious about the environment. Thus, one proposed alternative to this environmental drawback is ozonation. Like hypochlorite, ozone is an oxidant but it is also environmentally benign. Unfortunately, this method is extremely expensive. Ontario Hydro has estimated that use of ozonation would cost the corporation approximately $9 million per plant per year.
One member of the United States Fish and Wildlife Service estimates that the bill for re-engineering, maintenance and other forms of mussel abatement will total almost half a billion dollars per year. However, none of the current emergency measures, though they may alleviate specific problems on an ad hoc basis, will do anything to halt the overall proliferation of zebra mussels. The mussels are very strongly byssate and a mussel will attach to insides and occlude the openings of industrial and domestic pipelines, clog underground irrigation systems of farms, greenhouses, and any other facility that draws water directly from the Great Lakes, encrust navigation buoys to the point of submerging them, and encrust hulls of boats and other types of sailing craft that remain in the water over the summer and fall. The mussels may also form a significant vector of parasites that are lethal to game species of waterfowl and fish.
A United States Fish and Wildlife Service toxicologist reported in a news article featured in the November, 1991 issue of "Underwater USA" that the tiny but dreaded zebra mussel has been discovered for the first time in a section of the Mississippi River near La Crosse, Wis.
Another expert says that he expects to see the zebra mussel population explode by next year. Worse, it is likely boaters will inadvertently introduce the zebra mussel to the Minnesota lakes. The mussels have an extremely hard shell and clog water intakes at power plants and municipal water systems. The Monroe, Mich. water supply was crippled for three days when the mussels clogged a water intake pipe. As a result, water bills were increased eighteen percent to pay for the cost of removing them. An Ontario electric company spent $10 million on chlorine to keep the mussels out of its power plant water intake pipes. This expert expects the same things to happen at power and water plants on the Mississippi River. He states that locks and dams also are favored by the mussels, which have the potential to cause leaks and even to prevent control gates from closing completely.
The Applicant is aware of another material presently being marketed to control marine fouling of boat hulls. This material was developed by a chemical company in the eighties. Use of this material, however, is difficult and to date has not been tried on fluid transport systems. Also, the material requires a considerable amount of preparation of the substrate before it can be applied. Specifically, in terms of preparation, the material includes a primer. This primer is a very low viscosity, 100% epoxy undercoat. Like a wood preservative, the primer has a very high "wicking" characteristic. Thus, only one light coat of primer is required and it may be sprayed without thinning. Subsequently, one quart of the primer will cover approximately 400 square feet (approximately the wetted surface of a 42 foot full keel sailboat). This is a tack coat and should be applied similar to a wax as opposed to a paint application. A thick tack coat will cause the subsequent top coat of the material to run or bleed. The primer will cure to a "tacky" surface in 3 to 4 hours. It is only to be used as an undercoat and will oxidize if not covered with a finish coat. The finish coat may be applied at anytime after the surface becomes "tacky" to the touch, but should be applied within an eight hour time-frame window.
Preparation of the top coat material can now be discussed. This material is subject to settling and seven different ingredients are used to obtain its unique qualities of strength, flexibility, electrical-resistance, and anti-fouling properties. To assure uniformity, the epoxy base ("Part A") of the material must be thoroughly mixed to a homogenous "cake icing" consistency before adding the hardener or activator ("Part B"). Mixing should be done using an electric drill and a paint mixing agitator. It is a good practice to mix Part A each time prior to removing sub-lots from the primary container. If applicable, care should also be taken to ensure that the agitator has no protruding edges that may cut the plastic of the primary container. Experience has shown that plastic slivers can get in the mix and ultimately clog the spray nozzle. In addition, the hardener (Part B) must be thoroughly mixed before adding it to Part A. Three parts by volume of Part A, the epoxy base, is mixed with one part by volume of Part B, the hardener/activator. Ultimately at 70 degrees F. the mixture has the consistency of a dry wall joint compound. Heated to 110 degrees F. the consistency alters to that similar to a latex paint. The potlife at 70 degrees F. is about one hour, and at 105 degrees F. is about 20 minutes.
The material would now be ready for application. However, one serious concern with the material is that careful attention must be paid to the application time-frame window for the material. Specifically, the material should be applied while the primer is still "tacky". If the application window is missed, the surface should be re-profiled with 60-80 grit sandpaper, cleaned, and lightly covered again with the primer before proceeding. The material is then applied using a standard cup gun which is commonly used in automobile painting. Part A and Part B are added to the cup in the proper proportions and blended. Next, a 15-20% solvent is added to the cup and the cup is immediately closed. After tightly sealing the cup, the components are mixed by shaking and swirling the gun. A spray of approximately 60-80 psi air pressure is commenced.
In terms of the spray, a 0.001-0.002 inch thick tack coat is first sprayed over the primer and then followed within the next 10 to 45 minutes by a 0.004-0.005 inch thick coat. Next, a full 0.003-0.005 inch coat is applied until a finish thickness of 0.017-0.020 inch has been obtained. Re-coats may be applied every 10 to 15 minutes at 70 degrees F. Runs in the coats may occur if the prescribed applications are too thick, subjected to very warm environments, or exposed to direct sunlight. Lastly, another disadvantage of this material is that operator/applicator judgment becomes critical when the individual applications are done at less than ideal conditions.
If the cup gun does not have an agitator, the gun must be frequently shaken with a rapid wrist motion to keep a uniform mixture. Also, a pressure pot may be used for larger jobs. A working combination of a Bink's model 7 gun, a 2 gallon Bink's pot with agitator (model #83-5508), an air regulator (model #85-204) and a 38 PM nozzle have been used successfully in the application process. However, the 38 PM nozzle is quite large (about 0.086") and the operator may prefer a nozzle in the 0.060 range to obtain greater control of the overall film thickness.
The material should be allowed to cure for twenty-four to forty-eight (24 to 48) hours, depending on the ambient conditions prior to activation. The activation step is very important because barnacles will grow on any unactivated material. Next, the operator has options such as lightly sandblasting with either a wet or dry 40F grit or finer to activate the surface or to lightly sand with 220 wet/dry paper to remove blush. However, the longer the cure time before activation, the easier it will be to activate the material successfully. Optimally, the operator should allow the material to cure continuously for a week at 70 degrees F.
Finally, although the described material has been formulated for a high moist environment and will even cure underwater, for best results the material should not be applied to damp surfaces.
Although the above-mentioned technology has numerous inherent drawbacks such as the difficulties associated with the material's manufacture and application, the development of a method to successfully and simply coat specific components and existing structures would prove to be a viable method to prevent the adherence of organisms. Specifically, fluid transport systems which have components such as screens of various sizes cannot be fully lined, thus coating the structures will be a workable alternative. Coating will allow the water or fluid medium to pass through the porous openings or meshing of the screen but it will prevent the marine organisms from attaching.
A coating process will also prove to be invaluable in instances where components such as screens are small or located within (hard to reach) other structures such as valves. For instance, with screen components located within valves even a simplistic abrading technology would prove to be awkward and possibly even impossible to use. Thus, the best method for maintaining these structures would be attacking foreign substances or living marine organisms with a coating spray initially or retroactively applied to prevent the adherence and buildup of the foreign substance.
Therefore, based on the history and detrimental effects already known and attributed to the zebra mussel, it is apparent that it is critical to create a fluid transport system in which the pipes and other system components are coated with a material which would substantially minimize the initial adherence to and eventual buildup of foreign substances on the inner surfaces of the pipes and the exposed surfaces of other system components while they are submerged in a fluid medium.